The present invention relates generally to testing equipment and methods for measuring visual functions of the human vision system, and more particularly to an instrument and method for measuring visual capability under dim light, glare conditions.
The ability of a person to detect objects in the visual field is in part dependent upon the sensitivity to glare of that person's vision system. The degree of glare susceptibility of the human vision system is the overall effect of several contributing factors including the presence of light scattering particulate matter in the vitreous humor of the eye, congenital or injury induced cloudiness in the cornea or lens, the presence of cataracts, other changes in transparency of intraocular media due to the aging process, and similar and related factors.
The invention provides an instrument and method for measuring the susceptibility to glare of a human subject in a non-invasive manner. The instrument comprises a glare light source that also serves to illuminate a translucent acuity target. The housing for the light source and target includes a light baffle whereby light from the glare source is directed forwardly toward the subject and rearwardly through an optional optical filter for reflection off a mirror or diffusely reflective surface for transillumination of the acuity target disposed beside the glare source. The glare source is therefore observed by the subject simultaneously with the viewing of the acuity pattern. The observed glare obscures a portion of the pattern of the acuity target to a degree corresponding to the susceptibility to glare of the vision system of the subject. A single light source for both a glare source and acuity chart transillumination accords fixed calibration to the instrument. The instrument may be battery powered for portability.
The invention therefore provides a unique optical instrument and method for directly measuring visual acuity under substantially point source glare conditions, and, accordingly, may be highly useful in the assessment of certain physiological conditions of the normally transparent media of the eye. Further, the invention may be used for such purposes as monitoring post-surgical conditions of the eye, monitoring ocular trauma conditions or surgical or ophthalmic procedures, measuring severity of cataracts, defining analytical bases for glare susceptibility in individuals, and determining effects of contact lenses or other refractive elements on corneal physiology. The method of the invention is an ideal screening procedure for persons in night vision performance sensitive jobs such as night flying, refueling, driving, etc.
It is, therefore, a principal object of the invention to provide an instrument and method for measuring visual capability of the human vision system under dim light, glare conditions.
It is a further object of the invention to provide an instrument and method for measuring visual acuity of the human vision system under point source glare conditions.
It is yet another object of the invention to provide an improved chart for measuring visual acuity of the human vision system.
These and other objects of the invention will become apparent as the detailed description of certain representative embodiments thereof proceeds.